1. Field of the Invention
The present invention relates to power tools, e.g., tightening tools. In one aspect of the present teachings, techniques are described for accurately detecting the remaining battery capacity of a battery utilized to drive the power tool. In another aspect of the present teachings, techniques are described for accurately terminating a fastening operation using a tightening tool.
2. Description of the Related Art
When the battery utilized with a battery powered-tool is discharged below a certain voltage level, the battery should be recharged. In order to inform the power tool operator that the battery is due for recharging, Japanese Examined Utility Model Publication No. 4-32224 describes a power tool that provides a warning when the battery has been discharged below a certain voltage level.
The known power tool includes a light-emitting diode connected to a comparator. A voltage that is proportional to the battery voltage is input to one terminal of the comparator and a fixed reference voltage is input to the other terminal of the comparator. When the voltage that is proportional to the battery voltage exceeds the reference voltage, the light-emitting diode is not illuminated. However, when the voltage that is proportional to the battery voltage falls below the reference voltage, the output of the comparator changes, thereby causing the light-emitting diode to illuminate and warn the power tool operator that the battery is due to be recharged.